1. Field of the Invention
The present invention relates to a liquid crystal display device, and more particularly, to a light guiding structure for use in a liquid crystal display device.
2. Description of Related Art
A liquid crystal display device applies the electric field (E-field) to control the rotation of the liquid crystal molecules, and thus controls the polarization direction of the light to form light switches. The light-leaking regions in which the rotation of the liquid crystal molecules is hardly controlled (i.e. the liquid crystal alignment defect region) are usually shielded by the black matrix. The black matrix prevents the light leakage of these regions from impairing the contrast of the image.
Moreover, since the amorphous silicon layer of the thin film transistor is easily illuminated by the ambient light through the opening locating between the source electrode and the drain electrode of the thin film transistor. When the amorphous silicon layer of the thin film transistor is illuminated, a current is generated (i.e. the light-current), and the current leakage of the thin film transistor in the “non-conducting state” is increased. Therefore, in order to stabilize the correct gray-leveled displaying of each updating frame of image, a black matrix is required to dispose above the opening of the thin film transistor to block the ambient light and maintain the “non-conducting state” of the thin film transistor.
Currently, the black matrix (light-shielding element) is usually made of metal or non-transparent polymer material. However, there are several limitations and drawbacks related to the light-shielding elements. For example, the black matrix made of metal, such as chromium metal or chromium oxide (Cr/CrOx), causes heavy metal pollution and results in design limitation of the liquid crystal display device for the undesirable “parasitic capacitance”. On the other hand, the total thickness of the black matrix of polymers has to comply with the optical density of the polymer. For example, even though the optical density of the polymer is as large as four, the total thickness of the polymeric black matrix is still much thicker than that of the metal black matrix made. The black matrix with high thickness is not good for the structure of the liquid crystal display device. Besides, the rugged surface of the black matrix is not suitable for a rubbing process and the orientation of nearby liquid crystal molecules. Moreover, the efficiency of the lithography process is impaired for thicker material since the high thickness interferes the cross-linking of the polymer through the photo-chemical reaction. Therefore, the portion of the polymer material required to be kept after the lithography process is completely kept. The difficulty in manufacturing the black matrix made of polymer material thus increases.
Therefore, it is desirable to provide an improved liquid crystal display device to mitigate and/or obviate the aforementioned problems, which relates to the drawbacks of the manufacturing process of the liquid crystal display device and the black matrix thereof illustrated above.